lines while importing .dae files
These lines show relations between objects. I think in your case these are parent-child relations, which means that in the bottom left corner there is an object (parent) that, if you move it, moves all the other objects (children) with it.
You can disable that these lines are drawn.
In the Overlays for the viewport you can disable Relationship Lines.

Also have a look at the outliner window in the top right of your screen. It can tell you much about the scene:

If you expand the item by clicking on the small triangle left of the name of the object, you will see the objects that are parented.

If you want to make any of the parented object a completely independent object, then you can select it and press ⎇ Alt+P and clear the parent relationsip.


For Version 2.7
Press N while your mouse is in the 3D viewport to bring up the Properties shelf. Then scroll down to display and disable Relationship Lines:

If you also want to deactivate the transform widget look for the marked button at the bottom of your 3D viewport:

Alternatively you can activate Only Render. Then anything that is not mesh data will be hidden, except for the transform widget.